LHCb Wiki Pages - root

addclasstoroot

Anonymous (anonymous@undisclosed.example.com) — 2011-03-08T11:42:33+00:00

Adding A Class to ROOT Idea Instead of writing C++ macros which are intepreted by CINT, one can think of adding a class to ROOT itself. This may be particularly useful for methods that draw and save histograms, apply cuts, etc. The advantage over macros is the stability, as the code is compiled and then executed, and not interpreted by CINT.

addlegend

Anonymous (anonymous@undisclosed.example.com) — 2010-11-09T15:43:40+00:00

Adding a legend TLegend *legend = new TLegend(0.65,0.85,0.95,0.75); //xmin,ymin,xmax,ymax in percent from lower left corner legend->AddEntry(histogram1, "name1"); legend->AddEntry(histogram2, "name2"); legend->SetFillColor(kWhite); // otherwise you get an ugly grey background legend->Draw();

backcat

Anonymous (anonymous@undisclosed.example.com) — 2009-02-03T11:20:34+00:00

Categorizing Background using Monte Carlo truth Idea It may be useful to print the decay tree of a Monte Carlo particle that was associated to a reconstructed particle. Suppose you have a preselection and you want to see what particles the background, that passes your preselection, consists of. As your reconstruction

batchmode

Anonymous (anonymous@undisclosed.example.com) — 2009-03-13T09:53:59+00:00

Running ROOT in batch mode Idea Sometimes it may be useful to use ROOT without anything put on a canvas, e.g. if you want to run a script with nohup and then disconnect the ssh-connection. How to... You can start ROOT in batch mode with root -b

binsorder

Anonymous (anonymous@undisclosed.example.com) — 2011-03-18T11:33:22+00:00

What does "Bins must be in increasing order" mean It can mean, that: * Your (self set) bins are really not in increasing order, or: * The number of bins does not correspond to the array you give the histogram to set the bins, for example, you have to set:

chain

Anonymous (anonymous@undisclosed.example.com) — 2009-06-22T08:07:14+00:00

How to use chains in ROOT Idea A chain is sort of a container for trees. A chain can contain an arbitrary number of trees and can be used the same way as a tree, as the class chain inherits from the class tree. Adding Files A simple example is the following:

changemarkerstyle

Anonymous (anonymous@undisclosed.example.com) — 2010-11-09T15:04:58+00:00

Change Marker Style To change the marker style, you have to do: TGraph* myGraph = TGraph(); //... myGraph->Draw(); /** This is important */ myGraph->SetMarkerStyle(20); It will not work if the marker style is set before the graph is drawn. as your file will be empty.

colorscheme

Anonymous (anonymous@undisclosed.example.com) — 2010-08-24T15:10:54+00:00

Color scheme 255 Colors scheme To have 255 colors in the histograms, add the following to the root logon macro: const Int_t NRGBs = 5; const Int_t NCont = 255; Double_t stops[NRGBs] = { 0.00, 0.34, 0.61, 0.84, 1.00 }; Double_t red[NRGBs] = { 0.00, 0.00, 0.87, 1.00, 0.51 }; Double_t green[NRGBs] = { 0.00, 0.81, 1.00, 0.20, 0.00 }; Double_t blue[NRGBs] = { 0.51, 1.00, 0.12, 0.00, 0.00 }; TColor::CreateGradientColorTable(NRGBs, stops, red, green, blue, NCont); gStyle->SetNumberContours(NCont…

componentspyrootroofit

Anonymous (anonymous@undisclosed.example.com) — 2011-10-19T13:40:19+00:00

Drawing components of pdfs in RooFit with pyRoot Instead of doing: sum.plotOn(xframe, RooFit.Components(RooFit.RooArgSet(BG)), RooFit.LineColor(2)) you have to do: argset = RooArgSet(BG) sum.plotOn(xframe, RooFit.Components(argset), RooFit.LineColor(2))

controloutputroofit

Anonymous (anonymous@undisclosed.example.com) — 2012-02-22T10:42:41+00:00

Controlling the Output of RooFit In General The most systematic approach to controlling the output of RooFit is accessing the streams of the message service directly. The first thing is to check the instance of the RooMsgService: RooMsgService::instance().Print() ;

convpdgnumber

Anonymous (anonymous@undisclosed.example.com) — 2009-02-03T13:22:44+00:00

The convPDGnumber class Idea The C++-class convPDGnumber takes as an input the numbers of the Monte Carlo particle numbering schemes and provides information about them. The class is based on a list of all particles (PDGLaTeXTable.txt), according to the

custompdfsandworkspace

Anonymous (anonymous@undisclosed.example.com) — 2012-04-25T18:07:26+00:00

Custom PDFs and Workspaces Idea In RooFit you can define a custom PDF shape in a C++ class. This is a good idea if the model is widely used and speed is an issue. A popular example is the class “RooExpAndGauss”, which is used for partly reconstructed background in B decays. However, you need to be careful when defining these if you also want to deal with RooWorkspaces.

disk

Anonymous (anonymous@undisclosed.example.com) — 2009-12-08T09:02:45+00:00

root setup Setup root in the current directory and its subdirectories. Create a script setupROOT.sh containing: #!/bin/bash export MYSITEROOT=/app/lhcb/sw export CMTCONFIG=slc4_ia32_gcc34 export CMTPATH=$HOME/cmtuser export PATH=$MYSITEROOT/local/gcc-3.4.6/bin:$MYSITEROOT/local/binutils-2.15.92.0.2/bin:$MYSITEROOT/scripts:$PATH export LD_LIBRARY_PATH=$MYSITEROOT/local/gcc-3.4.6/lib:$MYSITEROOT/local/binutils-2.15.92.0.2/lib:$MYSITEROOT/lib:$LD_LIBRARY_PATH . $MYSITEROOT/LbLogin.s…

findbin

Anonymous (anonymous@undisclosed.example.com) — 2010-03-19T19:12:25+00:00

Find the bin the value corresponds to How to TH1D* bla = new TH1D("bla", "myHisto", 100,0,1); bla->FindBin(0,53); It also works for 2 or 3 dimensions.

functionsetnumberpoints

Anonymous (anonymous@undisclosed.example.com) — 2010-09-28T09:10:03+00:00

Set the number of points to draw a function Problem If you draw a function and zoom in, you see it is composed of straight lines connecting points. You can increase the number of points to solve this. Do TF1* func = new TF1("func","function", 0, 100); func->SetNpx(myNumberOfPoints);

labelstitle

Anonymous (anonymous@undisclosed.example.com) — 2010-11-09T15:41:16+00:00

Configure labels and title histo->GetYaxis()->SetLabelSize(.1); // font-size of Numbers on axis in percent of ??? histo->GetYaxis()->SetTitleSize(.12); // font-size for title in percent of ??? histo->GetYaxis()->SetTitleOffset(.2); // distance between axis and title in percent of normal distance histo->GetYaxis()->SetTitle("mySweetTitle");

lhcbroot

Anonymous (anonymous@undisclosed.example.com) — 2010-11-09T14:45:39+00:00

LHCb ROOT This page collects LHCb specific ROOT information. For general hints see ROOT. * Adding A Class to ROOT - how to add your own class (for analysis, drawing histograms,...) to ROOT * Store Monte Carlo particle numbers in a file - how to write a simple method that stores information about Monte Carlo particle numbers

loadtext

Anonymous (anonymous@undisclosed.example.com) — 2010-11-15T16:17:59+00:00

Read data from text file To read data from a text file into a tree all you need are the following two lines TTree *myTree = new TTree("mytree","data from ascii file"); Long64_t nlines = myTree->ReadFile(filename,"col1:col2:col3"); Dynamic Branche Names

logscale

Anonymous (anonymous@undisclosed.example.com) — 2010-11-09T15:36:00+00:00

Set log scale for an axis If a scale is displayed in log or normal scale is determined by the pad not the histogram! canvas->SetLogx(); pad->SetLogy(); Note that the axis letter (X, Y) are in lowercase.

nanfinite

Anonymous (anonymous@undisclosed.example.com) — 2009-02-18T09:10:33+00:00

Treatment of non-real numbers / infinity Idea If the result of a calculation in your code is an infinite number or an imaginary number, this may lead to problems (when drawing histograms, etc.). The following two methods help to catch these cases.

nostats

Anonymous (anonymous@undisclosed.example.com) — 2011-11-02T12:49:58+00:00

No StatBoxes gStyle->SetOptStat(kFALSE); from root import gStyle, kFALSE, kTRUE gStyle.SetOptStat(kFALSE)

numberofdivisions

Anonymous (anonymous@undisclosed.example.com) — 2010-11-09T15:37:15+00:00

How to Set the Number of Divisions in a TH1 Idea It may sometimes be useful to set the number of divisions for the axes of a TH1 in ROOT. How to Do: myhisto->GetXaxis()->SetNdivisions(ndiv, ) where ndiv = n1 + 100n2 + 10000*n3, where n1, n2, n3 are the number of primary, secondary and tertiary divisions. So 503 gives 3 main ticks, and 5 sub ticks between each of the main tick. And what is this option?

ownershippyroot

Anonymous (anonymous@undisclosed.example.com) — 2011-06-18T10:13:16+00:00

Ownership in PyROOT As python has a garbage collector, you have to make sure to pass on all objects that you want to keep. For example canvases. The following macro will produce 10 empty canvases and delete them in the end. from ROOT import * import ROOT for i in range(0,10): canv = TCanvas("canv"+str(i))

padlayouts

Anonymous (anonymous@undisclosed.example.com) — 2010-11-09T15:59:18+00:00

Examples of special padLayouts Two Histograms next to each other (vertically) TCanvas *canvas = new TCanvas("canvas","canvas"); pad1 = new TPad("pad1","",0,0.3,1,1); pad2 = new TPad("pad2","",0,0,1,0.3); pad1->Draw(); pad2->Draw(); pad1->cd(); pad1->SetBottomMargin(0.0); pad1->SetLogy(); pad1->SetGridx(); hist1->SetXTitle(xTitle); hist1->GetYaxis()->SetTitleSize(.05); hist1->GetYaxis()->SetTit…

padmargins

Anonymous (anonymous@undisclosed.example.com) — 2010-11-09T15:48:47+00:00

Change the Margins of a pad You can change the borders on a pad around a histogram by pad->SetTopMargin(0.0); // useful if you want to join two adjacent pads pad->SetBottomMargin(0.2); // in percent of the height

paletteaxis

Anonymous (anonymous@undisclosed.example.com) — 2011-06-23T16:26:34+00:00

The colour axis is an object of the type TPaletteAxis. Here the code i use to format it nicely: def ScaleZAxis(histname): hist = ROOT.gDirectory.Get(histname) ROOT.gPad.Update() palette = hist.GetListOfFunctions().FindObject("palette") palette.SetX1NDC(0.90) palette.SetX2NDC(0.92) palette.Draw() ROOT.gPad.Update()

pyrootgetevent

Anonymous (anonymous@undisclosed.example.com) — 2013-11-20T13:24:22+00:00

Accessing Events in a Tree To access the events in a tree no variables need to be assigned to the different branches. Instead the leaves are available as properties of the tree, returning the values of the present event. tree.GetEvent(0) print tree.Z0_MM # 18558.9 tree.GetEvent(1) print tree.Z0_MM # 2896.5

pyrootpassref

Anonymous (anonymous@undisclosed.example.com) — 2014-07-30T09:58:27+00:00

Pass by Reference # assuming graph is a TGraph from ROOT import Double x = Double(0) y = Double(0) graph.GetPoint(1, x, y)

python

Anonymous (anonymous@undisclosed.example.com) — 2014-02-12T15:17:32+00:00

Root and python TGraph from ROOT import * from numpy import array x = [1,2,3,4] # a list y = [5,6,7,8] # a list graph = TGraph(len(x),array(x,'f'),array(y,'f')) # convert lists to arrays

pythonrootconstructors

Anonymous (anonymous@undisclosed.example.com) — 2009-07-25T11:22:14+00:00

How use a ROOT constructor which needs pointers as arguments in python For example to create a histogram with variable bin width, the constructor needs a pointer to the array of the lowEdges (xbins). TH1D::TH1D(const char* name, const char* title, Int_t nbinsx, const Float_t* xbins)

pythonrootmacro

Anonymous (anonymous@undisclosed.example.com) — 2009-03-04T10:24:32+00:00

In your shell do: export PYTHONPATH=$PYTHONPATH:$ROOTSYS/lib:$ROOTSYS/root/pyroot Your python root macro should begin like this: from ROOT import * To run your macro: python -i filename.py

redrawaxis

Anonymous (anonymous@undisclosed.example.com) — 2013-08-23T14:55:09+00:00

Redraw axis to get Ticks on top When you draw several histograms on the same pad, later histograms will cover the axis drawn together with the first histogram. To redraw the axis on top, you can use Draw(“axis same”): hist1->Draw("Ep"); // to draw axis-range and label from hist1 hist2->Draw("hist same"); hist1->Draw("Ep same"); // to draw points on top hist1->Draw("axis same"); // to redraw axis

root

Anonymous (anonymous@undisclosed.example.com) — 2014-07-30T09:53:23+00:00

ROOT This page collects general ROOT hints. For LHCb specific info see LHCbROOT. Finding Help If you are looking for an example containing some specific class (TObjArray below). grep for it in the tutorial directory: cd $ROOTSYS/tutorials/ grep -r TObjArray *

rootlogonscript

Anonymous (anonymous@undisclosed.example.com) — 2008-12-01T15:41:19+00:00

Logon Script for ROOT When you start ROOT from commandline, it will execute the script rootlogon.C in the same directory. This may be useful when you want to load your own classes into ROOT or want to set some styles. Example Create a file named rootlogon.C (note the capital C), open it and write

saveplot

Anonymous (anonymous@undisclosed.example.com) — 2010-11-10T09:20:10+00:00

Save a plot to a file To save a file in a given format, you need to specify the format as parameter canvas->Print("filename.pdf","pdf");

setaxisrange

Anonymous (anonymous@undisclosed.example.com) — 2014-03-11T09:20:57+00:00

Set Display Range of Axis The normal way to change the display range of an axis is: histogram->GetYaxis()->SetRangeUser(lower,upper); but there are several situations where this fails. See below for help in these cases. Y Axis of a normalized Histogram

setup_most_recent_root_version_from_afs

Anonymous (anonymous@undisclosed.example.com) — 2010-11-15T10:36:49+00:00

Root is stored in afs at: /afs/cern.ch/sw/lcg/app/releases/ROOT/ select version and architecture (adapt first line) and set the following environment variables (code for bash): export ROOTSYS=/afs/cern.ch/sw/lcg/app/releases/ROOT/5.27.06/x86_64-slc5-gcc43-dbg/root #SLC 5 export ROOTSYS=/afs/cern.ch/sw/lcg/app/releases/ROOT/5.27.06/slc4_ia32_gcc34/root #SUSE 10 export PATH=$ROOTSYS/bin:$PYTHONDIR/bin:$PATH export LD_LIBRARY_PATH=$ROOTSYS/lib:$PYTHONDIR/lib:$LD_LIBRARY_PATH export PYTHONPATH=…

setxaxisrangetgraph

Anonymous (anonymous@undisclosed.example.com) — 2010-11-06T14:06:18+00:00

Set the range of the x axis in a TGraph Problem If you have a TGraph, SetRangeUser will not work for the x axis. TGraph* myGraph = new TGraph(); ... myGraph->SetRangeUser(lower,upper); will not complain but also not do anything. Or not the thing you want.

showcuts

Anonymous (anonymous@undisclosed.example.com) — 2010-01-12T10:26:40+00:00

Show cut value as a line in a histogram To create a line in a histogram for example to indicate a cut do the following in your python root macro and in the canvas where you have the histogram: cutObj = TLine(XcutValue, hist.GetMinimum(), XcutValue, hist.GetMaximum()) cutObj.SetLineColor(kGreen+2) cutObj.SetLineWidth(2) cutObj.Draw("lsames")

splash

Anonymous (anonymous@undisclosed.example.com) — 2010-11-09T15:12:03+00:00

Splash Screen You can get rid of the splash screen when starting root by using the -l flag: $ root -l You might want to set this as an alias in your shells rc-file (.cshrc, .bashrc) alias root='root -l' # bash alias root 'root -l' # csh

storemcnumbers

Anonymous (anonymous@undisclosed.example.com) — 2009-01-07T14:16:46+00:00

Storing Monte Carlo particle numbers in a file Idea When analyzing signal or background using Monte Carlo truth information, it may be useful to check the real identity of a particle that was considered a Kaon, a Muon, etc. The following script loops through the whole tree, calculates the percentage of the respective particle and saves the output in a textfile. It needs as input the tree with the truth-information (e.g. in an nTuple) and the name of the variable. Furthermore, the name of the …

strings

Anonymous (anonymous@undisclosed.example.com) — 2010-11-10T11:01:04+00:00

String manipulation For more details see the TString Reference. Substring Get substring of existing string TString new = old(start, subStrLength); // start is the index of the first character // subStrLength is the number of characters to copy // e.g: remove S charachters form start and E from end TString new = old(S, old.Length()-S-E);

style

Anonymous (anonymous@undisclosed.example.com) — 2010-11-09T15:45:47+00:00

Change Style of Canvas/Pad To get plots without any backgrounds use //void myMacro(myArgList) { gROOT->SetStyle("Plain"); In macros this needs to be given inside the function to have an effect.

thstack

Anonymous (anonymous@undisclosed.example.com) — 2012-08-16T09:58:07+00:00

Using and Troubleshooting THStack Basic Code TH1F *h; THStack *hs = new THStack("hs","Stacked 1D histograms"); //create three 1-d histograms for (int i = 0; i < 3; i++) { h = new TH1F("h"+i,"test hstack",100,-4,4); h->FillRandom("gaus",20000-i*5000); h->SetFillColor(i+2); h->SetMarkerColor(i+2); hs->Add(h); } TCanvas *cst = new TCanvas("cst","stacked hists",10,10,700,700); cst->SetFillColor(41); hs->Draw()

troubleshooting

Anonymous (anonymous@undisclosed.example.com) — 2013-06-14T10:14:15+00:00

Root-files Root-files can be the source of various problems. Usually they are caused by hidden changes in the internal state of ROOT. ROOT stores the active directory and uses this to create new objects and look for existing ones. The active directory is changed when a new file is opened. This can lead to unexpected behaviours and hard to trace bugs.

ttreedraw

Anonymous (anonymous@undisclosed.example.com) — 2013-06-14T09:41:58+00:00

TTree::Draw() Basic Usage The Draw()-Method of TTrees is a very useful tool to quickly create histograms. The following code creates a histogram with the default settings. TFile file("myfile.root"); TTree *tree = file.Get("mytree"); tree->Draw("myvar");

two_stats_boxes

Anonymous (anonymous@undisclosed.example.com) — 2009-03-27T13:56:38+00:00

How to overlay tow histograms and draw both stats boxes void myfunction() { ... TCanvas *c = new TCanvas(...) TH1D *h1 = new TH1D(...) ; // histo 1 TH1D *h2 = new TH1D(...) ; // histo 2// set stats options (show histo title, nEntries, mean, rms) gStyle->SetOptStat(1111);